As computers become more ubiquitous throughout our environment, the desire to make computers and their interfaces even more user friendly continues to promote development in this area. For example, the MIT Media Lab, as reported by Brygg Ullmer and Hiroshi Ishii in “The metaDESK: Models and Prototypes for Tangible User Interfaces,” Proceedings of UIST10/1997:14-17,” has developed another form of “keyboardless” human-machine interface. The metaDESK includes a generally planar graphical surface that not only displays computing system text and graphic output, but also receives user input by responding to an object placed against the graphical surface. The combined object responsive and display capability of the graphical surface of the metaDESK is facilitated using infrared (IR) lamps, an IR camera, a video camera, a video projector, and mirrors disposed beneath the surface of the metaDESK. The mirrors reflect the graphical image projected by the projector onto the underside of the graphical display surface to provide images that are visible to a user from above the graphical display surface. The IR camera can detect IR reflections from the undersurface of an object placed on the graphical surface.
By detecting a specially formed object or IR-reflected light from an object disposed on a graphical display surface, the metaDESK can respond to the contemporaneous placement and movement of the object on the display surface to carryout a predefined function, such as displaying and moving a map of the MIT campus.
Others have been developing similar keyboardless interfaces. For example, papers published by Jun Rekimoto of the Sony Computer Science Laboratory, Inc., and associates describe a “HoloWall” and a “HoloTable” that display images on a surface and use IR light to detect objects positioned adjacent to the surface.
The interactive display systems described above, as well as other interactive display systems, generally employ separate optical systems for each of three different purposes. A first optical system is used to project images and data onto the display surface. A second optical system is used to evenly distribute IR light over the display surface to illuminate physical objects disposed adjacent to the display surface. A third optical system is used to receive and focus IR light reflected or generated by physical objects disposed adjacent to the display surface to detect user inputs.
Understandably, using multiple optical systems to carry out these functions adds bulk and cost to an interactive display system. In addition, using multiple, separate optical systems typically requires steps to be taken to correct for any misalignment of the respective images between the different optical systems. For example, if the image projected by the first optical system onto the display surface with which the user will interact is not aligned with the third optical system that is imaging the IR light produced by the user's inputs, the resulting projected and imaged input will be offset from each other. It will thus be necessary to correct for the offset to avoid errors in interpreting the user input relative to the projected image to which the user's input is directed. Conventional interactive systems of this type do not provide an efficient approach to avoid this problem.